This study examines the phenomenon of mother-infant separations that occur in the course of normal family life as contrasted with those that occur as a result of hospitalization or family crisis. Four categories of separation were identified: (1) those due to mother's employment, (2) those due to mother's scheduled, nonreimbursed activities (discretionary activities), (3) those involving overnight separation, and (4) non-scheduled brief separations. Rates of occurrence for all four types were high in a sample of 144 mothers and their first-born infants, indicating that mother-infant separation is a normal aspect of infancy in our culture. The data clearly show that maternal employment and mother-baby separation cannot be equated. Although infants with employed mothers experienced significantly more separation, on the average, than did infants whose mothers engaged only in discretionary activities, there was an overlap in the amount of separation experienced by these groups. Furthermore, among infants with employed mothers, there was great variation in the amount of separation that occurred, ranging from none to nearly sixty hours per week. In order to examine some of the factors which may mediate the effects of separation, characteristics of employment-related and discretionary activity-related separations were compared. Significant differences were found between these two types of experience across a wide range of theoretically important intervening variables. These included frequency and duration of separations; patterning (predictability) of the experience; baby's age; number, identity and familiarity of caregivers; number of substitute care locations; number of other children being simultaneously cared for by the substitute caregiver; and mother's subjective sense of comfort with the separation and care arrangements. The findings indicate a variety of ways in which separation experiences can be differentiated, thus allowing for more specific empirical evaluation of effects on children.